The recrystallization of polar solutes with marginal solubility in non-polar solvents is known. For relatively pure solutes, enhancing solubility by increasing the temperature of the solvent may be sufficient to effect a suitable recrystallization result. However, conventional methods of recrystallization may be unsuitable for mixtures in which impurities are present, or more than one solute is employed, or an insoluble substance is present during recrystallization, since the nature of mixtures is to prevent or retard crystal growth of selected ingredients. As a result, small size crystals and small size dispersed particles cannot be consistently and reproducibly obtained using conventional recrystallization techniques.
The recrystallization of organic solids to produce small crystals, leading to powders and dispersions of small particle size, i.e., ranging from less than one to about twenty-five microns, is important in several formulation-based industries. As used herein, a formulation-based industry is an industry whose products are based on mixtures of ingredients, in which each ingredient retains most of its original chemical properties despite being combined with the other ingredients. Such industries include, but are not limited to, those which produce personal care products, cosmetics, and over-the-counter drug formulations such as antiperspirants and sunscreens.
Conventional dispersion methods such as high speed, high shear stirring and solvent recrystallization are widely used in these industries, but these methods do not readily create a uniform dispersion of very small particle size unless the solid component has been micronized by prior processing, or has undergone purification processing, or has been processed through expensive and time-consuming specialized equipment, e.g., high-pressure homogenizers.
Therefore, there exists a need in the formulation-based industries to reduce the particle size of certain ingredients, and to formulate with such ingredients in either powder form or dispersed form, without premicronization or purification processing or specialized equipment. This has become especially evident in the personal care and cosmetics industries, the latter in particular for the formulation of sunscreens and cosmetics containing sunscreens.
Due to the increasing use of both natural and synthetic organic ingredients, the personal care industries and especially the cosmetics industry have recently been seeking a greater degree of perceived topical benefits from products applied directly onto the stratum corneum. These benefits include lubricity, evenness of application, spreadability, lack of oiliness or stickiness, greater skin adhesion and a more comfortable, even pleasant, skin feel.
Thus, a need exists in the cosmetics and personal care industries for new formulations of fine particle size powders and dispersions, and for processes to produce such formulations that are efficient, effective, and yield products with a uniform particle size that are comfortable to use. In the case of cosmetics, sunscreens and sunscreen-containing cosmetics, a need exists for formulations that are lubricous, have a non-oily, non-greasy, non-sticky, pleasant skin feel, and are efficacious in that the expected Sun Protection Factor ("SPF") value of a sunscreen formula is not impaired.
Accordingly, it is an object of the present invention to provide improved processes for producing small particle size powders, and recrystallized mixtures and dispersions of small crystal size, that function as active ingredient delivery systems within the types of industries described.
Another object of the invention is to provide an improved process by which to recrystallize an insoluble active ingredient, thereby affording the formulator substantial ease of use when incorporating such an active ingredient into finished product formulae.
Still another object of the invention is to provide improved fine particle size powders, mixtures and dispersions.
A further object of the invention is to provide improved topical ingredients for personal care products such as cosmetics and sunscreens that are lubricous and aesthetically pleasing to the skin.
Yet another object of the invention is to provide lubricous mixtures that are efficacious, particularly in the active ingredient delivered.